An electro-photographic printer having a developing cartridge detachably mounted therein is well known in the art. Conventionally, this type of printer is provided with a sensor for detecting whether a mounted developing cartridge is a new product.
As one example of such printers, Japanese Patent Application Publication No. 2011-215374 discloses a laser printer including a main casing and a developing cartridge. The main casing is provided with an actuator and an optical sensor. The developing cartridge includes a detected rotary body and an agitator gear. The detected rotary body is provided with a disc-shaped gear part having gear teeth along a portion of its circumferential surface and a tooth lacking part, and a detected part erecting on a left endface of the gear part. The agitator gear is provided with a large-diameter gear part configured to receive a drive force, and a small-diameter gear part configured to intermesh with the gear teeth of the disc-like gear part of the detected rotary body.
In this conventional laser printer, a drive force is transmitted to the detected rotary body via the agitator gear. Upon receipt of the drive force, the detected rotary body is rotated so that the detected part is brought into abutment with the actuator to pivotally move the same. Upon detection of the pivotal movement of the actuator by the optical sensor, the laser printer can determine information on the developing cartridge.